review of the lunar laser ranging technique and contribution of timing systems

Abstract

The lunar laser ranging (LLR) technique is based on the two-way time-of-flight of laser pulses from an earth station to the retroreflectors that are located on the surface of the moon. We discuss the ranging technique and contribution of the timing systems and its significance in light of the new LLR station currently under development by the Hartebeesthoek Radio Astronomy Observatory (HartRAO). Firstly, developing the LLR station at HartRAO is an initiative that will improve the current geometrical network of the LLR stations which are presently concentrated in the northern hemisphere. Secondly, data products derived from the LLR experiments -such as accurate lunar orbit, tests of the general relativity theory, earth-moon dynamics, interior structure of the moon, reference frames, and station position and velocities -are important in better understanding the earth-moon system. We highlight factors affecting the measured range such as the effect of earth tides on station position and delays induced by timing systems, as these must be taken into account during the development of the LLR analysis software. HartRAO is collocated with other fundamental space geodetic techniques which makes it a true fiducial geodetic site in the southern hemisphere and a central point for further development of space-based techniques in Africa. Furthermore, the new LLR will complement the existing techniques by providing new niche areas of research both in Africa and internationally.

Time delay in the quadrupole field of a body at rest in the 2PN approximation

“…For instance, both Lunar Laser Ranging (LLR) as well as Satellite Laser Ranging (SLR) have reached the subnano-second and even the pico-second level of accuracy [18][19][20][21][22][23] which implies a standard deviation of the atomic clocks of about ∆t/t ∼ 10 −13 . In these experiments a laser signal is sent from a ground station to the Moon or satellite, where it is reflected from retroreflectors, and then the laser signal is received back by the ground station; a review of LLR and future developments of SLR are given in [21,24]. Meanwhile, there exists a global network of 45 active ground stations which represent the International Laser Ranging Service.…”

Lunar Radiometric Measurement Based on Observing China Chang’E-3 Lander with VLBI—First Insight

“…Compared with LRM in Apollo era, precision of LLR has increased from orders of decimeters to less than 2 cm [3,30]. Errors in the coordinates of the lunar beacons of ALSEPs 14 and 15 on the other hand are closer to 1m, and ALSEPs 12, 16, and 17 may have errors as large as 30m [31].…”

“…Since the first successful spacecraft "lunar 2" reached lunar surface by Soviet Union in 1959, more than 100 missions have been undertaken to research the Moon [2]. In 1969, the Apollo program started a new era for studying the Moon, such as determining parameters of the lunar orbit, physical librations, interior structure, and Earth-Moon dynamics [3]. Since then, LLR (Lunar Laser Ranging) Operation has been conducted to the retroreflector arrays at the Apollo 11, 14, and 15 sites plus the French-built reflector on the Soviet Lunokhod 1 and 2.…”

A spatiotemporal analysis of the effect of ambient temperatures on the thermal behaviour of the Lunar Laser Ranging optical telescope at Hartebeesthoek Radio Astronomy Observatory

“…Various components of the LLR telescope are currently being integrated at HartRAO (Combrinck, 2011) coupled with the installation of modern instrumentation and development of sub-systems for operating the optical telescope (Tsela et al, 2016, Munghemezulu et al, 2016, Combrinck and Botha, 2013. This telescope is a classical Cassegrain system ( Figure 1) comprising various component materials such as Zerodur, Aluminium T6 7075 and Low carbon steel 1023 with varying thermal properties (Tsela et al, 2015).…”

“…Development of the new LLR geodetic station is underway at the Hartebeesthoek Radio Astronomy Observatory (HartRAO) of South Africa. This station is planned to acquire enhanced (millimetre) Earth-Moon distance measurements in the Southern Hemisphere (Munghemezulu et al, 2016) using the refurbished ex-French 1-metre aperture telescope (Combrinck and Botha, 2013); and would be an addition to the five capable LLR stations based in the Northern Hemisphere (Noda et al, 2014), namely the McDonald Observatory (Texas, U.S.A), Observatoire de la Côte d'Azur (France), Apache Point Observatory (New Mexico, U.S.A.), Matera (Italy) and Wettzell (Germany). Considering the uneven distribution of capable LLR stations worldwide, the HartRAO LLR station would play a significant role in the continuous global monitoring of the Earth-Moon system dynamics, as well as understanding the processes in the complex Earth system.…”